"snapcraft clean <part>" fails if the files I asked it to clean don't exist

[Alistair Buxton]

Steps to reproduce:

Make a directory and save attached snapcraft.yaml in it.
snapcraft
snapcraft clean pulseview

Expected result:
All build/stage/prime etc artifacts for the pulseview part are deleted.

Actual result:

al@al-desktop:~/Source/sigrok-snap-test$ snapcraft clean pulseview -s prime
"grade" property not specified: defaulting to "stable"
Cleaning priming area for pulseview
[Errno 2] No such file or directory: '/home/al/Source/sigrok-snap-test/prime/meta/gui/pulseview.desktop'

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: snapcraft 2.29
ProcVersionSignature: Ubuntu 4.4.0-77.98-generic 4.4.59
Uname: Linux 4.4.0-77-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: XFCE
Date: Thu May 11 13:47:09 2017
InstallationDate: Installed on 2015-07-12 (669 days ago)
InstallationMedia: Xubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422.1)
PackageArchitecture: all
SourcePackage: snapcraft
UpgradeStatus: Upgraded to xenial on 2016-06-30 (315 days ago)

[Alistair Buxton (a-j-buxton)]

Attaching the snapcraft.yaml in case the git repo changes.